while the remaining resistances R3 and R4 are placed between
A H and H K respectively. The battery B is connected to AK,
and the galvanometer to H D. The thermometer being set to
freezing point, the pointer D is xotated till at D, and the resistance
r is adjusted till the galvanometer G reads zero. DX then indicates
32° F, or o° C, according to the scale adopted. If N be now
subjected to a higher temperature, G will be out of balance till D
be sufficiently raised, and the point on the circle where balance is
restored will show true temperature of N, for the leads ee and bb
are mutually opposing resistances, and the net result wfil be the
resistance of coil N only. The platinum thermometer gives
consistent readings up to about 1000° C. or 1800° F. It is also
very delicate, and very respondent, the changes being taken up
without any measurable lag, and it is equally, true for high or
.low temperatures. By balancing N'S resistance against one
slightly less,, a dead-beat galvanometer will autographically trace
a temperature-time curve (see p. 876).
P. 590* Combination of Boyle's and Charles' Laws.
—The formula P V oc r can be rigidly proved by step-by-step
process. In the following columns the pressure, volume, and
absolute temperature of a gas are gradually changed, the first
three lines under Boyle's law, where pressure x volume is
constant and temperature invariable; and the last two lines under
Charles' law, where volume -T- absolute temperature is constant,
and pressure invariable. In either case multiply or divide out the
respective columns and verify.
Pressure. Volume. Abs. Temp.